In semiconductor integrated circuit manufacturing, it is conventional to test the integrated circuits (“IC's”) during manufacturing and prior to shipment to ensure proper operation. Wafer testing is a well-known testing technique commonly used in production testing of wafer-mounted semiconductor IC's (or “dice”), wherein a temporary electrical current is established between automatic test equipment (ATE) and each IC (or die) on the wafer to demonstrate proper performance of the IC's. Components often used in wafer testing include an ATE test board, which is a multi-layer printed circuit board that is connected to the ATE, and that transfers the test signals back and forth between the ATE and a probe card.
With reference to FIG. 1, a conventional probe card (aka a probe card assembly) includes a printed circuit board (PCB) (not illustrated) having contacts in electrical communication with several hundred probes/probe elements or needles 10 positioned to establish electrical contact between a tip portion 12 of each of the probes 10 and a series of connection terminals (or “die contacts” or “electrodes” or “pads” or “electrode pads”) 20 on the IC wafer (or “semiconductor device”) 30. Known probe cards further include a substrate 40 (e.g., a space transformer 40) which electrically connects the probes to the printed circuit board. The substrate 40 may include, for example, a multi-layer ceramic substrate, or a multi-layer organic substrate. It is known to mount each of the plurality of flexible probes 10 to a mounting surface of the substrate 40. Typically, the probes 10 are mounted to electrically conductive, preferably metallic bonding pads formed on the substrate 40 through conventional plating or etching techniques well known to those of ordinary skill in the art of semiconductor fabrication. Alternatively, it is known to mount the probes 10 within a probe head assembly which positions ends of the probes in electrical communication with contacts on the substrate/space transformer surface.
Semiconductor geometry is constantly decreasing. For example, electrodes 20 may be 50 micrometers by 50 micrometers in size and the on-center distance between the electrodes 20, otherwise known as the pitch, may be approximately 75 micrometers. In order to contact only one electrode 20 at a time, a probe needle 10 of a small diameter is desired. The probe 10 should be large enough in diameter to provide the mechanical stability and support necessary to keep the probe needle 10 from bending excessively. However, because of the small size of the electrodes 20, it is desirable that the probe tips be pointed or needle-like. Probes 10 may be made of many different materials, as is known in the art, and in one embodiment may be made of tungsten. Other materials used for probes 10 include nickel alloys, paliney, beryllium copper, tungsten-rhenium, palladium alloys, and silicon in combination with a metal coating.
With continued reference to FIG. 1, electrode 20 of semiconductor device 30 may be formed of aluminum (Al) or other metallic materials known in the art, such as aluminum-silicon-copper pads, gold pads, and lead/tin bumps. An aluminum oxide layer, or other oxide layer, may form over the surface of electrode 20 during the wafer manufacturing process. Because aluminum oxide is an insulator, if present, it is desirable to scratch through the oxide layer so that a reliable contact is formed between the electrode 20 and the probe tip 12. Scratching through the oxide layer may be accomplished by an “overdrive” process. The probe tip 12 is brought in to contact with the wafer electrode 20, and then “overdriven” an additional amount, moving the probe 10 closer to the electrode 20, and increasing the contact force between the probe tip 12 and the electrode 20. The overdrive process may also include relative lateral movement between the probe 10 and the wafer 30, allowing the probe tip 12 to more readily scrape the surface of the electrode, and to breach any oxide layer.
The overdrive process may break through the oxide layer to make a good electrical connection with the electrode; however, extraneous particles such as aluminum, aluminum oxide, silicon, and other types of particles, debris or foreign matter may adhere to the surface of the probe tip 12. After repeated probing operation, the particles on the probe tip 12 may prevent a good conductive connection from forming with electrode 20 and the probe tip 12. The repeated probing process may also cause the probe tip 12 to become blunted. A blunt probe tip may make the probe tip 12 less effective at scratching the surface of the electrode 20. A blunted probe tip may also cause probe marks to go beyond the specified allowable electrode contact area on the wafer if the blunt end of the tip becomes too large. A pointed probe tip has a smaller tip surface area at the end of the probe tip such that, for the same force, a higher pressure can be applied on the aluminum oxide, providing for an enhanced ability to break through the aluminum oxide.
A further problem related to the blunting of a probe tip 12 is that uneven blunting of probe tips creates probes of different lengths leading to planarity problems. Probes 12 may wear unevenly because sometimes some of the probes may be probing portions of the wafer where no electrodes exist and the probes touch down on materials of different hardness than the electrode pad 20. Additionally, probe tips 12 may have burrs formed when the probes were made or sharpened, or from adhered debris. Probes 10 may also be uneven in length for other reasons. Regardless of the reason for the variability in the probe tip lengths, planarity problems decrease the ability of the probes to properly contact the target electrode pads. Some efforts to improve planarity involve the blunting of non-blunted probe tips to conform to the length of the already blunted tips. This, however, negatively impacts the performance of the probe cards in other respects as discussed herein.
In response to the problem of particles adhering to the probe needle 10, a number of techniques have been developed for cleaning probe tips 12. For example, U.S. Pat. No. 6,170,116 (i.e., the '116 patent) discloses an abrasive sheet which is composed of a silicon rubber which provides a matrix for abrasive particles, such as an artificial diamond powder. The '116 patent discloses that upon insertion of a probe into the abrasive sheet some of the extraneous particles that adhere to the probe tip may be removed or scraped off by the abrasive particles. Unfortunately, this process may not remove all of the extraneous particles from the probe tip and may contaminate the probe tip with a viscous silicon rubber film or other particles which adhere to the tip as it is stuck into the silicon rubber matrix. To counteract this secondary particle contamination of the tip, the probe needle may be cleaned by spraying an organic solvent onto the tip of the needle, thereby dissolving and removing some of the viscous silicon rubber film and perhaps some of the secondary particles. Thereafter, the organic solvent may be blown off the probe tip in order to further prepare the tip. This process is time consuming and is performed off-line. Furthermore, the process may result in particles stuck to the tip and even introduce further contaminates.
Other wafer cleaning devices are disclosed. A cleaning wafer with a mounted abrasive ceramic cleaning block, which is rubbed against the probe needles, is disclosed in U.S. Pat. No. 6,019,663. The use of a sputtering method to remove particles from the probe tip is disclosed in U.S. Pat. No. 5,998,986. The use of a rubber matrix with abrasive particles and a brush cleaner made of glass fibers is disclosed in U.S. Pat. No. 5,968,282. Use of lateral vibrational movement against a cleaning surface for removing particles from a probe tip is disclosed in U.S. Pat. No. 5,961,728. Spraying or dipping the probe needles in cleaning solution is disclosed in U.S. Pat. No. 5,814,158. Various other cleaning methods are disclosed in U.S. Pat. Nos. 5,778,485 and 5,652,428.
Many of these methods and devices interrupt the testing of wafers by use of off-line processing to clean the probe tips. Some of these methods introduce further contaminates to the probe tips. Some of these methods exacerbate the blunting of the probe tips. None of these methods adequately address the shaping of probe tips while cleaning on-line. Probe tip shaping extends the life of the probe needle, and enhances the scratching ability, thereby enhancing the reliability of the electrical contact.
Therefore, it would be desirable to provide an on-line method and apparatus to clean particles from probe tips without the use of solvents or blowing mechanisms. Furthermore, it would be desirable to provide a method and apparatus for cleaning probe tips that does not blunt the tip of the probes, but rather enhances the shape of the probe tip. Additionally, it would be desirable to provide the ability to clean and shape the probe tips in a quick and consistent manner with minimal downtime.